1. Field of the invention
The present invention relates to the rotor of a turbomachine, and in particular to the means by which the blades are fixed on the rotor.
2. Summary of the prior art
Several methods are currently used to effect the fixing and radial retention of the movable blades mounted on the high speed rotor discs or drums of modern turbomachines. It is usual for the blades to be constituted by a vane Proper having an aerodynamic shape which ensures the required performance for a compression or turbine stage, and a base comprising a root above which there may be a platform defining the inner wall of the main flow path of the gases. This root, which may be, for example, hammer or fir-tree shaped, is fitted in a cooperating axial groove provided on the rim of a rotor disc or on the outer periphery of a rotor drum. In some cases, the fixing may instead be in a peripheral or circumferential direction. In all cases complementary means usually ensure locking of the blades in the different radial, axial and peripheral directions.
These early solutions, which are well known and still widely used, particularly in aeronautical applications both in the military and civil fields, are not, however, fully satisfactory when applied to aircraft engines of the new type, particularly those in which the gas generator is associated with an additional power turbine of low rotational speed intended to drive either a fan or a propeller, and comprising in particular two contra-rotating stages. As a result of the reduction in rotational speed, and therefore also of the stress level to which the rotating parts are subjected, a lighter system than the previously used techniques can be used. This aim for lightness is accompanied by a search for simplification, particularly so as to make assembly easier. Finally, taking into account the new conditions of operation, good stability of the low speed parts of the rotor must be obtained.
Certain elements of the present solution which, however, in themselves are inadequate, may be found in earlier arrangements which have not reached the degree of complexity and sophistication of some more recent, better known solutions. For example, U.S. Pat. No. 2,654,565 describes the mounting of blades of which the base has shoulders constituting hooks cooperating with slits formed in the rims of discs assembled to form a rotor, and U.S. Pat. No. 3,063,674 discloses the use of rivets for fixing the rotor blades.